What brand portable generators does costco sell?

Sign Champion Generac

I don't know, go on line or call.

Cummins, Generac, Ativa, Honeywell, Yeti, Champion, Ubio Labs, A-I Power, Firman .... etc.

Champion and Generac, have seen both.

I know Genetac

Champion and Generac at most locations. Some sell firman and others.

You can call and ask... it depends on tghd location